The human eye is made up of three coats, enclosing three transparent structures.
The outermost layer is composed of the sclera and the cornea. The sclera, also known as the white of the eye, is an opaque and fibrous layer that protects the eye, while the cornea is the transparent front part of the eye that covers the iris, pupil and anterior chamber. The cornea, with the anterior chamber and lens, refracts light. Therefore, the sclera and the cornea have very different intrinsic properties.
The middle layer consists of the choroid, the ciliary body which is the thickened anterior portion of the choroid, and the iris. The iris is composed of circular muscle fibers that constrict the pupil and radial muscle fibers that dilate the pupil.
The innermost layer is the retina, which is mainly composed of the neural tissue including photoreceptor cells that receive and process incoming light.
Within these coats are the aqueous humour, the vitreous body, and the flexible lens. The aqueous humour is a clear fluid that is contained in two areas: the anterior chamber between the cornea and the iris, and the posterior chamber between the iris and the lens. The lens is suspended to the ciliary body by the suspensory ligament, made up of fine transparent fibers. The vitreous body is a clear jelly that is much larger than the aqueous humour present behind the lens, and the rest is bordered by the sclera, zonule, and lens. They are connected via the pupil.
Document WO 2005/115281 describes an ocular iontophoresis device for applying active substances to an eye. FIG. 1 shows such a device 200.
Such a device 200 comprises an active electrode 201, a reservoir 202, and at least one medication 203 stored in the reservoir 202, a passive electrode 204 enabling the electric circuit to be looped, and an electrical power supply 205 delivering DC to the electrodes 201 and 204.
The reservoir 202 is delimited laterally by a wall 206 defining a tubular-shaped body and comprising a distal end 207 configured for being positioned on an ocular surface 208 of the eye and surrounding the cornea 209 and a part of the sclera 210.
The device 200 is therefore adapted for treating the sclera 210 and the cornea 209 simultaneously.
However, as described above, the sclera and the cornea have very different intrinsic properties. In particular, the maximum tolerable current density for the cornea 209 is about 2 mA/cm2, while the maximum tolerable current density for the sclera 210 is about 10 mA/cm2. Furthermore, medication molecules having a size greater than 1.500 Da are not able to penetrate into the cornea 209, while medication molecules having a size lower than 150.000 Da are able to penetrate into the sclera 210.
Therefore, the intrinsic properties of the cornea 209 usually impose the medication and the current density to be applied by the active electrode 201 for treating simultaneously the cornea 209 and the sclera 210.
Therefore, there is a need for developing an ocular iontophoresis device configured for treating simultaneously the cornea and the sclera whilst taking into account intrinsic properties of each ocular tissue.
Document WO2012/162459 also describes an iontophoresis device of the state of the art. This device comprises a first chamber and a second chamber having annular shapes with the second chamber being inside the first chamber, so that first and second chambers form concentric rings. First and second chambers are further configured for receiving the medication(s). The first chamber and the second chamber are respectively connected to a first electrode and a second electrode configured for being in communication with the medication(s) received in the first and the second chambers, respectively. In this document, when the device is positioned on the eyeball of a patient, the first chamber surrounds the cornea of the eyeball, while the second chamber is between the first chamber and the cornea of the eyeball. Therefore, such a device is only configured for treating the sclera of the eyeball. As a result, this document is only dedicated to the treatment of the sclera and does not address the technical problem of treating simultaneously the cornea and the sclera whilst taking into account intrinsic properties of each ocular tissue.
Document US2012/0201800 describes another example of an iontophoresis device of the state of the art. This device comprises an outer ring electrode and an inner ring electrode, associated with an outer reservoir and an inner reservoir, respectively. In this document, the outer electrode and the inner electrode are configured for being positioned on the sclera surrounding the cornea, when the device is positioned on the eyeball of a patient. Therefore, such a device is only configured for treating the sclera of the eyeball. As a result, this document is only dedicated to the treatment of the sclera and does not address the technical problem of treating simultaneously the cornea and the sclera whilst taking into account intrinsic properties of each ocular tissue.